The present invention relates generally to gas turbine engines, and, more specifically, to turbine nozzles therein.
A gas turbine engine includes a compressor for pressurizing air which is then mixed with fuel in a combustor and ignited for generating hot combustion gases. The combustion gases are discharged from the combustor through a high pressure turbine nozzle which directs the gases to a row of first stage high pressure turbine blades mounted in the perimeter of a supporting disk. The turbine blades extract energy from the gases for rotating the disk and in turn rotating a shaft joined to the compressor.
The gases from the high pressure turbine are then channeled downstream into a low pressure turbine which includes an additional turbine nozzle and corresponding row of turbine blades for extracting additional energy from the gases which is used for producing useful work. For example, the low pressure turbine may be connected to a fan disposed upstream of the compressor in a typical turbofan aircraft engine application. Or, the low pressure turbine may be joined to an output shaft for producing output work in industrial and marine engine applications.
The high pressure turbine nozzle first receives the hot combustion gases from the combustor and must be suitably mounted for ensuring efficient operation of the engine and a suitably long life during use notwithstanding the hostile environment in the high temperature combustion gases. A typical turbine nozzle is formed of arcuate segments including outer and inner bands typically having multiple stator vanes integral therewith. The vanes are hollow for channeling cooling air bled from the compressor during operation.
The outer and inner bands must be suitably mounted to stator elements in the engine while minimizing undesirable flow leakage therethrough which would decrease engine performance during operation. And, aerodynamic and thermal loads and stresses therefrom must be accommodated for ensuring suitable life.
The individual nozzle segments are typically sealed to each other using conventional spline seals, and the outer and inner bands are suitably sealed to adjoining stator elements. For example, the inner band may include a radial mounting flange bolted to an annular inner casing located below the combustor. Bolting effects contact seals between the flange and inner casing, however, the bolting restrains thermal growth of the nozzle elements causing increased thermal stress which affects nozzle life.
Alternatively, the mounting flange may include a retention pin instead of a bolt without the clamping forces associated with the latter which cradle mounts the nozzle segments and permits axial rocking thereof as the outer and inner bands are subject to differential axial thermal expansion and contraction relative to the adjoining supporting elements.
Cradle mounting permits the individual nozzle segments to thermally expand and contract without clamped restraint, and therefore substantially reduces thermal stresses associated therewith.
However, cradle mounting requires suitable features for carrying to the supporting stator elements axial, tangential, and radial loads developed in the turbine nozzle during use. Rocking of the mounting flange must be effected without undesirable vibratory instability and without excessive fretting wear of contact surfaces subject to rocking or pivoting movement. Fretting is a particular concern along circumferential lands through which radial loads are carried between the nozzle and supporting elements. And, undesirable flow leakage through the various contact faces subject to rocking and pivoting, in particular at the retention pins, must be minimized for reducing performance penalties.
Accordingly, it is desired to provide a turbine nozzle mounting reducing fretting wear and contact seal losses.
A turbine nozzle includes a row of vanes in corresponding segmented outer and inner bands. The inner band of each segment includes a retention flange. A nozzle support includes forward and aft flanges defining a retention slot receiving the retention flange. The retention flange includes a radial lug trapped axially in the retention slot, and a tangential lug at an opposite circumferential end disposed on the forward flange. The aft flange includes an outer hinge, and the retention flange further includes an inner hinge for cradle mounting the retention flange in the nozzle support.